<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>太极八卦</title>
  <style>
    #yin-yang {
      width: 96px;
      height: 48px;
      background: #eee;
      border-color: red;
      border-style: solid;
      border-width: 2px 2px 50px 2px;
      border-radius: 100%;
      position: relative;
    }

    #yin-yang:before {
      content: "";
      position: absolute;
      top: 50%;
      left: 0;
      background: #eee;
      border: 18px solid red;
      border-radius: 100%;
      width: 12px;
      height: 12px;
    }

    #yin-yang:after{
      content: "";
      position: absolute;
      top: 50%;
      left: 50%;
      background: red;
      border: 18px solid #eee;
      border-radius: 100%;
      width: 12px;
      height: 12px;
    }

  </style>
</head>
<body>
<div id="yin-yang"></div>
</body>
</html>
